1. Field of the Invention
The present invention relates to a fuse structure used in an integrated circuit device, and more particularly, to a novel fuse structure having a backup conductive layer.
2. Description of the Related Art
Fuses are routinely used in the design of monolithic integrated circuits (IC), and in particular in memory devices as elements for altering the configuration of the circuitry contained therein. As such, memories are commonly built with programmed capabilities wherein fuses are selectively xe2x80x9cblownxe2x80x9d by, e.g., a laser beam.
It is well known that random access memories (RAM) are designed with redundancies which include spare columns, rows, or even fully functional arrays, wherein when any of these spare elements fails, the defective row, column and the like are replaced by a corresponding element. Disabling and enabling of spare elements is accomplished by fuses which are blown (i.e., melted away) when required, preferably, by a laser beam.
Additionally, the technique of laser fuse deleting (trimming) has been widely used both in the memory and logic IC fabrication industries, as an effective way to improve functional yields and to reduce development cycle time. Yet, fuse blow yield and fuse reliability have been problematic in most conventional fuse designs.
FIG. 1 is a sectional view of a traditional fuse structure. FIG. 2 is a top view of a traditional fuse structure. And FIG. 1 shows the cross section C-Cxe2x80x2 of FIG. 2.
Referring to FIG. 1, symbol 100 shows an insulated layer substrate. A metal layer M0 is formed on part of the substrate 100. An oxide layer 120 is formed on the metal layer M0 and part of the substrate 100. A metal layer M1 having an optimal position of laser spot 110 is formed on part of the oxide layer 120. At least one conductive plug 130 is defined through the oxide layer 120, for electrically connecting the M0 layer and the M1 layer. A fuse window 140 is formed above part of the M1 layer comprising the position 110 and part of the oxide layer 120. Symbol 150 shows a passivation layer.
In FIG. 2, there are plural fuse structures 210, 220, 230 in the fuse window 140. Each fuse structure 210, 220, 230 comprises the M0 layer, the plug 130 and the M1 layer. The solid line area shows the M1 layer, the dash line area shows the M0 layer, and each structure 210, 220, 230 comprises its own optimal position of laser spot 110. To give an example, a laser beam 290 blows the position 110 of the fuse structure 220. Because of misalignment of the laser beam 290 or thermal scattering of the laser beam 290, thermal shock from the laser blow process can damage the M0 layer of the fuse structures 210, 230, located near the fuse structure 220. This can cause the fuse structures 210, 230 to crack, seriously affecting device reliability and yield.
An object of the present invention is to provide a novel fuse structure. An optimal position of laser spot is defined above a substrate. A first conductive layer is formed on part of the substrate. A first dielectric layer is formed on the substrate and the first conductive layer. A second conductive layer is formed on the first dielectric layer. A second dielectric layer is formed on the first dielectric layer and the second conductive layer. A third conductive layer comprising the position of laser spot is formed on part of the second dielectric layer. A plurality of first conductive plugs penetrate the first dielectric layer, to electrically connect the first conductive layer and the second conductive layer. At least one second conductive plug penetrates the second dielectric layer, to electrically connect the second conductive layer and the third conductive layer.
The present invention improves on the prior art in that the first conductive layer, serving as a backup conductive layer, is placed under the second conductive layer. Thus, the invention can prevent the fuse structure from failing when both misalignment of the laser beam and thermal scattering of the laser beam damage the second layer of the fuse structure in the laser blow process, raises reliability and yield, and ameliorates the disadvantages of the prior art.